1. Field of the Invention
The present invention relates in general to wireless communications infrastructures, and in particular, to systems and methods for implementing antenna hopping and redundancy with multi-carrier power amplifiers and combining schemes within a base station.
2. Description of the Related Art
In wireless communication systems, two approaches have evolved to combat small scale fading of the mobile radio channel caused by multipath propagation. To increase receiver performance, either adaptive antennas or diversity schemes can be employed. One such diversity scheme is called “antenna hopping”. Antenna hopping has proven to be particularly useful and effective for small spectrum applications, typically providing potential gains of up to 10-30% in network capacity.
In antenna hopping, consecutive bursts of information are transmitted on different antennas in an antenna array located in a single Base Transceiver Subsystem (BTS). A diversity gain is achieved because multi-path transmission significantly reduces the probability that the signal components will fade simultaneously. The diversity gain is most pronounced in low mobility conditions, i.e., when mobile stations are moving slowly. FIG. 1 is a functional block diagram illustrating the elements of a BTS configured to implement an antenna hopping scheme. To achieve additional performance improvements, an antenna hopping scheme is often combined with a frequency hopping scheme, which involves applying different frequency bands (shown as f1 through f6) to different antennas in an alternating sequence.
Increasing capacity demand with respect to a particular cell often dictates the need for the deployment of more signal carrying transceivers (TRXs) at the corresponding BTS. To maintain full coverage for the area served by the cell, the output signals from the TRXs are preferably combined and then amplified and otherwise optimized. If the TRX output signals are not combined, an excessive number of feeders connecting each TRX to the antenna are required, possibly exceeding the structural capabilities of the cell tower.
Commonly, the TRX output signals are combined using low power combiners. Then, a device such as a high power ultra linear wideband Multi-Carrier Power Amplifier (MCPA) amplifies each of the transmitted signals so that the signals can be received over a desired area.
Antenna hopping inherently requires parallel sets of antennas, as well as other equipment such as amplifiers, combiners, and duplexers (DPXs). For a small number of radios, this capital equipment can become prohibitively expensive, particularly because a single MCPA may cost several thousand dollars.
Furthermore, an additional level of redundancy of BTS hardware is desirable to maximize system reliability. For instance, a dedicated backup MCPA known as a “hot standby” is often deployed as a backup—taking over in the event of failure of the active MCPA for a particular antenna. Maintaining a hot standby MCPA and associated hardware for each antenna or set of antennas is an expensive solution. One alternative for maintaining system reliability is to provide full redundancy without antenna hopping or transmit diversity. Obviously, however, redundancy without diversity does not address the problem of signal fading. There is a need, therefore, to create a system and methodology that provides for both diversity and redundancy without incurring the prohibitive cost associated with previous systems for providing such redundancy.